1. Field of the Invention
The present invention relates in general to an electrical heater, and more particularly to a thermo-sensitive heater used in various kinds of mats or blankets.
2. Description of the Related Art
Conventional electric products such as electric mats and electric mattresses include one or more temperature sensors arranged in a laminated mat having a heater. A temperature controller in the heater detects a heating temperature of the heater by the temperature sensor, compares the detected temperature with a preset temperature, and controls caloric power of the heater. The conventional electric product, designed to control the temperature of its heater as described above, has a problem that the price of the product is increased due to the use of the temperature sensors and sensor connecting wires. Such a conventional electric product also has a problem that the product does not meet the electromagnetic wave safety standards because electromagnetic waves are undesirably radiated from the lead wires extending between the sensors and the temperature controller.
The term xe2x80x9cheating elementxe2x80x9d, xe2x80x9cheating wirexe2x80x9d or xe2x80x9cheaterxe2x80x9d is intended to mean a cord-shaped heating material having flexibility, and coated with synthetic resins for protection, for being arranged in a heating product such as an electric mat, an electric blanket, an electric cushion, an electric bed, socks, and etc, and being used to perform the heating function of such products.
According to the prior art, a generally used non-magnetic heating wire is disclosed in Korean Utility Laid-open Publication No.97-64561. This electromagnetic wave attenuation heater has an insulation layer interposed between inner and outer coiled heating wires, with the ends of the wires connected to each other such that the directions of currents flowing in the conducting wires within a heating element are opposite to each other, and thereby the electronic waves from the wires can be offset. Consequently, the directions of circular magnetic fields surrounding the heating coils are also opposite to each other, and thereby the intensity of magnetic field from the heating coils can be decreased. However, even in a case of using the non-magnetic heating wire, there are generated electric fields, which fatigue the nervous system of a body. It is also common knowledge that magnetic fields prevent a person from sleeping soundly by affecting brain waves. Therefore, a method of eliminating the electric field in heaters must be devised.
Further, an electromagnetic wave removing apparatus has been proposed and used for discharging electromagnetic waves to the ground. An electromagnetic wave discharging apparatus is applied to various kinds of electric mats, as well as electric products having the electromagnetic wave attenuation heater. In the construction of such electromagnetic wave discharging apparatuses, an electromagnetic wave shielding element, such as a copper net and etc., is installed in an electric product such that the shielding element surrounds the heater inside the electric product. In such a case, the copper net used as the shielding element is connected to the ground. The installation of a copper net in an electric product for removing the electromagnetic waves from the product is problematic in that it wastes materials, complicates the production process, and increases the weight and cost of the product, thus deteriorating the competitive power and design flexibility of the product.
For the foregoing reasons, there is a need for a heater that reduces electromagnetic radiation without requiring increased amount of materials and cost of production.
Accordingly, the present invention is directed to a thermo-sensitive heater and heating circuit that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
It is an object of the present invention to provide a thermo-sensitive heater having both a nylon thermistor and an electric field shielding coil within a cord-shaped heater and operates such that its temperature controller detects the temperature of the heating element, and controls the driving current for a heating coil.
It is another object of the present invention to provide a thermo-sensitive heater for controlling a heater driving current without a separate temperature sensor.
It is still another object of the present invention to provide a driving circuit for safely driving the heater.
It is still another object of the present invention to provide a driving circuit having an overheating prevention circuit.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a thermo-sensitive heater comprises a nylon thermistor arranged on a middle layer between a cord-shaped heating element and an electrical insulation coating layer for detecting a temperature of the heating element, and having a negative temperature characteristic. A current supplying terminal is connected to one of inner and outer surfaces of the nylon thermistor, and a temperature detecting terminal is connected to the other of the inner and outer surfaces of the nylon thermistor for controlling a driving current for the heating element by a temperature controller.
According to one aspect of the preferred embodiment of the present invention, the nylon thermistor is tubular and is formed on an outer surface of the cord-shaped heating element through an extrusion forming process and an inner side of the thermistor is connected to a heating coil which is also used in part as a temperature detecting terminal.
According to another aspect of the preferred embodiment, the thermo-sensitive heater employs a driving circuit.
In an alternative embodiment of the present invention, a thermo-sensitive heater having a heating element inside it, and having a coating layer with electric insulating and waterproofing means on its outside, comprises a cord-shaped nylon layer, as a thermo-sensitive device, that surrounds an entire heating element, a first electrode contacted with an inner surface of the nylon layer, a second electrode connected to an outer surface of the nylon layer, an electric insulation layer for surrounding the entire surfaces of the cord-shaped nylon layer, and a first shielding coil wound around entire surfaces of the electric insulation layer.
According to one aspect of the alternative embodiment, the first electrode is used as a heating coil and the second electrode is used as a second shielding coil where the heating element is a non-magnetic heating element.
According to another aspect of the alternative embodiment, the thermo-sensitive heater employs a driving circuit.
According to another aspect of the alternative embodiment, resistors within the circuit are arranged to heat a temperature fuse.
In another alternative embodiment of the present invention, wire meshes are used as electrodes and/or electric fields shields.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide a further explanation of the invention as claimed.